Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Gain access to PCB (use Insulation Mat as required)
Run hot water tap until water cool then turn tap OFF
DHW temperature selector to MAX
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset appliance as necessary.
Allow the ignition sequence to commence and burner to ignite.
While measuring the voltage between the pins with the brown wire and blue wires at connector X14 on the PCB turn the DHW temperature control to MINIMUM to disable preheat.
Does the mains voltage disappear immediately or does the PCB continue to send voltage to the gas valve after the demand ends?